Conventionally, as an apparatus that displays/projects images, a projector that projects an image generated by a liquid crystal panel onto a screen is known. There is a technique for displaying a single image on a large screen using a plurality of such projectors (see, for example, Japanese Patent Laid-Open No. 2005-286772). FIG. 13 shows an example of a configuration for projecting a single image using a plurality of projectors. In FIG. 13, reference numeral 1301 indicates an image splitter, 1302 to 1305 indicate projectors, and 1306 to 1309 indicate projected images projected by the projectors 1302 to 1305. The projected images 1306 to 1309 are combined so that a single image is displayed. By using a plurality of projectors, it is possible to project high resolution large-screen images as compared to the case of using one projector.
Also, for image display apparatuses such as projectors and television sets, a technique called dynamic gamma correction for executing an optimal tone correction process for each video scene has been devised (see, for example, Japanese Patent Laid-Open No. 8-317250). This is a technique in which correction is performed on input data according to the pixel distribution in each scene and the magnitude of changes between scenes so as to visually optimize each scene image.
In the case where one projector is used, by performing a scene adaptive process such as dynamic gamma correction described above, optimal correction can be performed. However, in the case where an image is projected using a plurality of projectors as in Patent Document 1, a situation may sometimes occur in which it is not possible to perform an appropriate process on the entire image. This will be described with reference to FIG. 13 and FIGS. 14A to 14D.
In FIG. 13, the original image is divided by the splitter 1301 and input to the projectors. Each projector analyzes only an image that it will project, and performs a scene adaptive process such as dynamic gamma correction. Each projector first calculates a luminance histogram of the input image for the scene adaptive process. Examples of luminance histograms are shown in FIGS. 14A and 14B.
FIG. 14A shows an example of a luminance histogram of the image 1306 projected by the projector 1302. FIG. 14B shows an example of a luminance histogram of the image 1309 projected by the projector 1304. The projector 1302 determines gamma characteristics thereof based on the luminance histogram shown in FIG. 14A. In the case of the luminance histogram of FIG. 14A, for example, the distribution concentrates on a high luminance portion, and therefore gamma characteristics are determined such that tones in the high luminance portion are expressed. An example of the gamma characteristics is shown in FIG. 14C. Likewise, the projector 1304 determines gamma characteristics thereof based on the luminance histogram shown in FIG. 14B. In the case of the luminance histogram of FIG. 14B, the distribution concentrates on a low luminance portion, and therefore gamma characteristics are determined such that tones in the low luminance portion are expressed. An example of the gamma characteristics is shown in FIG. 14D.
As described above, in the case where each projector performs a scene adaptive process by analyzing only a divided image output from the splitter 1301, a situation occurs in which different correction processes are applied because gamma characteristics vary within one image (1306 to 1309), which results in an unnatural tone balance in the entire image.